Treatment fluids comprising an alkali metal complexing agent and methods for use thereof

ABSTRACT

Alkali metal ions may lead to the production of insoluble materials during the course of stimulating a subterranean formation, particularly when acidizing a siliceous formation or a formation containing a siliceous material. Alkali metal ions may be sequestered using an alkali metal complexing agent in order to reduce their propensity toward forming insoluble materials in a subterranean formation. Methods for stimulating a subterranean formation can comprise: providing a treatment fluid that comprises an alkali metal complexing agent comprising a cyclic polyether having between 3 and 6 ether oxygen atoms present therein, and hydrofluoric acid, a hydrofluoric acid-generating compound, or any combination thereof; and introducing the treatment fluid into a subterranean formation.

CROSS-REFERENCE TO RELATED APPLICATIONS

The present application is a divisional of U.S. patent application Ser.No. 13/444,897, filed on Apr. 12, 2012.

BACKGROUND

The present disclosure relates to stimulation of subterraneanformations, and, more specifically, to treatment fluids that can lessenthe opportunity for alkali metal ions to produce insoluble materialsduring the course of performing a stimulation operation.

Treatment fluids can be used in a variety of subterranean treatmentoperations. Such treatment operations can include, without limitation,drilling operations, stimulation operations, production operations, sandcontrol treatments, and the like. As used herein, the terms “treat,”“treatment,” “treating,”and grammatical equivalents thereof refer to anysubterranean operation that uses a fluid in conjunction with achieving adesired function and/or for a desired purpose. Use of these terms doesnot imply any particular action by the treatment fluid or a componentthereof. Illustrative treatment operations can include, for example,fracturing operations, gravel packing operations, acidizing operations,scale dissolution and removal, consolidation operations, and the like.

In acidizing operations, a subterranean formation containing anacid-soluble material can be treated with an acid to dissolve at least aportion of the material. Formation components of the formation matrixmay comprise the acid-soluble material in some cases. In other cases,the acid-soluble material may have been deliberately introduced into thesubterranean formation in conjunction with a stimulation operation(e.g., proppant particulates). Illustrative examples of formationcomponents that may be dissolved by an acid include, for example,carbonates, silicates, and aluminosilicates. Dissolution of theseformation components can desirably open voids and conductive flowpathways in the formation that can improve the formation's rate ofhydrocarbon production, for example. In a similar motif, acidization maybe used to remove like types of precipitation damage that can be presentin the formation.

Carbonate formations often contain minerals that comprise a carbonateanion (e.g., calcite). When acidizing a carbonate formation, the acidityof the treatment fluid alone can be sufficient to solubilize theformation components. Both mineral acids (e.g., hydrochloric acid) andorganic acids (e.g., acetic and formic acids) can be used to treat acarbonate formation, often with similar degrees of success.

Siliceous formations can include minerals such as, for example,zeolites, clays, and feldspars. Most sandstone formations, for example,contain about 40% to about 98% sand quartz particles (i.e., silica),bonded together by various amounts of cementing material includingcarbonates (e.g., calcite), aluminosilicates, and other silicates. Asused herein, the term “siliceous” refers to a substance having thecharacteristics of silica, including silicates and/or aluminosilicates.

Acidizing a siliceous formation (e.g., a sandstone formation or aclay-containing formation) or a formation containing a siliceousmaterial is thought to be considerably different than acidizing acarbonate formation. Specifically, the treatment of a siliceousformation with the treatment fluids commonly used for acidizing acarbonate formation may have little to no effect, because mineral acidsand organic acids do not effectively react with siliceous materials. Incontrast to mineral acids and organic acids, hydrofluoric acid can reactvery readily with siliceous materials to produce soluble substances.Oftentimes, a mineral acid or an organic acid can be used in conjunctionwith a hydrofluoric acid-containing treatment fluid to maintain thetreatment fluid in a low pH state as the hydrofluoric acid becomesspent. In some instances, the low pH of the treatment fluid may promoteinitial silicon dissolution and aid in maintaining the silicon in adissolved state. At higher subterranean formation temperatures (e.g.,above about 200° F.), it may be undesirable to lower the pH much belowabout 1 due to mineral instability that can occur. Additionally,regardless of the formation temperature, corrosion can be an inevitableproblem that occurs when very low pH treatment fluids are used.

Although low pH treatment fluids may be desirable to aid in silicondissolution, precipitation of insoluble fluorosilicates andaluminosilicates can still become problematic in the presence of certainmetal ions. Specifically, under low pH conditions (e.g., below a pH ofabout 3), dissolved silicon can react with Group 1 metal ions (e.g., Na⁺and K⁺) to produce insoluble fluorosilicates and aluminosilicates. Theterms “Group 1 metal ions” and “alkali metal ions” will be usedsynonymously herein. Other metal ions, including Group 2 metal ions(e.g.,

Ca²⁺ and Mg²⁺), may also be problematic in this regard. Theprecipitation of insoluble fluorosilicates and aluminosilicates canblock pore throats and undo the desirable permeability increaseinitially achieved by the acidizing operation. That is, the formation ofinsoluble fluorosilicates and aluminosilicates can damage thesubterranean formation. In many instances, the damage produced byinsoluble fluorosilicates and aluminosilicates can be more problematicthan if the acidizing operation had not been conducted in the firstplace. In contrast to many metal ions, ammonium ions (NH₄ ⁺) are notbelieved to promote the formation of insoluble fluorosilicates andaluminosilicates. Accordingly, treatment fluids comprising an ammoniumsalt are frequently used in conjunction with acidizing a siliceousformation, as discussed further below.

Problematic alkali metal ions or other metal ions can come from anysource including, for example, the treatment fluid, a component of thetreatment fluid, or the subterranean formation itself. For example, thecarrier fluid of a treatment fluid may contain some sodium or potassiumions unless costly measures (e.g., deionization) are taken to limittheir presence. Alkali metal ions, in particular, are widely distributedin the environment and can be especially difficult to avoid completelywhen conducting a subterranean treatment operation. As discussed furtherbelow, a variety of strategies have been developed to address the mostcommon sources of problematic metal ions encountered when conductingsubterranean treatment operations.

One strategy that has been used with some success to avoid the damagingeffects of metal ions includes introducing a sequence of pre-flushtreatment fluids into the subterranean formation prior to performing anacidizing operation with a hydrofluoric acid-containing treatment fluid.For example, a pre-flush treatment fluid comprising a mineral acid or anorganic acid can be used to dissolve acid-soluble formation componentsand remove at least a portion of the problematic metal ions from theformation. Thereafter, another pre-flush treatment fluid comprising anammonium salt can be introduced into the subterranean formation todisplace the remaining formation metal ions and leave the formationenriched in ammonium ions. Although this approach can be usedsuccessfully, it can considerably add to the time and expense needed toperform an acidizing operation.

Another strategy that can be used to mitigate the effects of metal ionsin acidizing operations is to introduce a chelating agent into thesubterranean formation. Although this strategy can be successful forGroup 2 metal ions and transition metal ions, for example, chelation isbelieved to be somewhat less effective for alkali metal ions. Inaddition, many chelating agents are utilized in their salt form, whichis many times their Na⁺ or K⁺ salt form. Thus, use of a chelating agent,although reducing precipitation effects from certain metal ions, canactually exacerbate the precipitation effects of alkali metal ions.Sometimes the free acid or ammonium salt forms of chelating agents canbe used to avoid this issue, at least in principle, but the free acidand/or ammonium salt forms of many chelating agents are either unknownor not commercially available at a reasonable cost. Furthermore, manycommon chelating agents are not biodegradable or present other toxicityconcerns that can make their use in a subterranean formationproblematic.

Crown ethers are one class of compounds that has been shown to have goodproperties for sequestering (complexing) alkali metal ions. Conventionalcrown ethers comprise a cyclic polyether macrocycle, where themacrocyclic ring size can dictate its selectivity for complexingdifferent alkali metal ions. Although crown ethers have been usedextensively in chemical synthesis, cost and toxicity issues associatedwith these compounds have tempered their use elsewhere. Azacrown ethers,which have one ether oxygen atom replaced with nitrogen, can showenhanced selectivities and binding affinities compared to crown ethers,but they are more expensive still. Most likely due to cost factors, itis not believed that either of these types of compounds have heretoforebeen contemplated for use in subterranean treatment operations,particularly to mitigate the precipitation of fluorosilicates andaluminosilicates that may occur in conjunction with an acidizingoperation.

SUMMARY OF THE INVENTION

The present disclosure relates to stimulation of subterraneanformations, and, more specifically, to treatment fluids that can lessenthe opportunity for alkali metal ions to produce insoluble materialsduring the course of performing a stimulation operation.

In some embodiments, the present invention provides a method comprising:providing a treatment fluid that comprises: an alkali metal complexingagent comprising a cyclic polyether having between 3 and 6 ether oxygenatoms present therein; and hydrofluoric acid, a hydrofluoricacid-generating compound, or any combination thereof; and introducingthe treatment fluid into a subterranean formation.

In some embodiments, the present invention provides a method comprising:providing a treatment fluid that comprises: an alkali metal complexingagent comprising a pseudocrown ether; forming a complex of thepseudocrown ether with an alkali metal ion; and introducing thetreatment fluid into a subterranean formation.

In some embodiments, the present invention provides a method comprising:providing a treatment fluid having a pH ranging between about 0 andabout 8 that comprises: an alkali metal complexing agent comprising apseudocrown ether; introducing the treatment fluid into a subterraneanformation; and performing an acidizing operation in the subterraneanformation.

In some embodiments, the present invention provides a treatment fluidcomprising: an alkali metal complexing agent comprising a pseudocrownether; hydrofluoric acid, a hydrofluoric acid-generating compound, orany combination thereof; and optionally, a chelating agent, an alkalimetal salt of a chelating agent, a non-alkali metal salt of a chelatingagent, or any combination thereof.

The features and advantages of the present invention will be readilyapparent to one having ordinary skill in the art upon a reading of thedescription of the preferred embodiments that follows.

DETAILED DESCRIPTION

The present disclosure relates to stimulation of subterraneanformations, and, more specifically, to treatment fluids that can lessenthe opportunity for alkali metal ions to produce insoluble materialsduring the course of performing a stimulation operation.

As described above, metal ions, especially alkali metal ions, can leadto a number of issues when present during an acidizing operation.Particularly in the presence of dissolved silicon (e.g., in the form ofSiF₄, SiF₅ ⁻, or SiF₆ ²⁻), alkali metal ions can result in damagingalkali fluorosilicate precipitates. Current approaches to dealing withthe issue of fluorosilicate and aluminosilicate precipitation can becostly and may be insufficient in some cases.

The present disclosure describes alkali metal complexing agents that canbe included in treatment fluids to be used in conjunction with anacidizing operation or other stimulation operation. As used herein, theterm “alkali metal complexing agent” refers to a compound that forms areaction product with an alkali metal. The alkali metal complexingagents can sequester problematic alkali metal ions, such that they areless available to react with dissolved silicon to form insolublematerials. Treatment fluids comprising an alkali metal complexing agent,as described herein, can further comprise hydrofluoric acid, ahydrofluoric acid-generating compound, or any combination thereof, orthe treatment fluid can be introduced into a subterranean formationahead of or subsequent to a treatment fluid comprising hydrofluoricacid, a hydrofluoric acid-generating compound, or any combinationthereof. Thus, treatment fluids comprising an alkali metal complexingagent may be used in response to alkali metals that are present atvarious stages of the treatment process.

Without being bound by any theory or mechanism, it is believed thatalkali metal complexing agents can react with alkali metal ions toproduce a complex that is less reactive than the free alkali metal ion.Accordingly, the alkali metal ions may be less capable of reacting withdissolved silicon to produce insoluble materials. More specifically,during an acidizing operation conducted in a siliceous formation or aformation containing a siliceous material, alkali metal complexingagents may limit the ability of alkali metal ions to react and forminsoluble alkali metal fluorosilicates and aluminosilicates, which candamage the formation.

Applicant does not believe that there has been any contemplation in theart to use alkali metal complexation as a means for controllingprecipitation within a subterranean formation. Crown ethers and azacrownethers are well known alkali metal complexing agents that have been usedin other applications, such as chemical synthesis. However, as describedabove, their use in subterranean treatment operations may have beentempered by factors including cost and toxicity, for example.

Other types of alkali metal complexing agents that are related to crownethers and azacrown ethers may address the potential disadvantagesassociated with the latter two classes of compounds. Pseudocrown ethers,for example, may be a particularly suitable alternative to crown ethersand azacrown ethers. The term “pseudocrown ether,” as used herein,refers to a crown ether analogue that has an ether oxygen moiety of theparent crown ether structure replaced with a carbon-containing moiety.For example, in some embodiments, the carbon-containing moiety may be amethylene group. Other functionalization and derivatization of theparent crown ether structure may also be present in pseudocrown etheranalogues. Pseudocrown ethers suitable for use in the embodimentsdescribed herein are described in further detail below.

In the context of treating a subterranean formation, pseudocrown ethersmay allow particular advantages to be realized over crown ethers orazacrown ethers. First, pseudocrown ethers encompass a wide structuralclass that may be synthesized by a number of known macrocyclizationtechniques. Some pseudocrown ether structures may be more easilysynthesized than are the parent crown ethers, which may allow certainpseudocrown ethers to be produced at a lower cost than other types ofalkali metal complexing agents. In addition, pseudocrown ethersreportedly have a reduced toxicity profile relative to crown ethers. Thereduced toxicity profile may make pseudocrown ethers moreenvironmentally acceptable for conducting subterranean treatmentoperations.

A number of advantages can be realized when using a treatment fluid thatcomprises an alkali metal complexing agent. Although such treatmentfluids described herein may be particularly advantageous when used inconjunction with an acidizing operation, they may be used at any stageduring the treatment of a subterranean formation. For example, treatmentfluids comprising an alkali metal complexing agent may be used inconjunction with a stimulation operation (e.g., a fracturing operation),with a further stimulation operation being conducted at a later time(e.g., an acidizing operation using a treatment fluid comprisinghydrofluoric acid and/or a hydrofluoric acid-generating compound). Sucha treatment sequence may leave the subterranean formation desirablydepleted in free alkali metal ions, such that they are less available toinduce fluorosilicate and aluminosilicate precipitation once acidizingbegins. In some embodiments of the present invention, a treatment fluidcomprising an alkali metal complexing agent may be introduced into asubterranean formation before or subsequent to a treatment fluidcomprising hydrofluoric acid, a hydrofluoric acid-generating compound,or any combination thereof. In more preferred embodiments of the presentinvention, particularly for acidizing operations, the separate treatmentfluids may be combined into a single-stage treatment fluid thatcomprises both an alkali metal complexing agent and hydrofluoric acid, ahydrofluoric acid-generating compound, or any combination thereof.

A primary advantage of using a treatment fluid comprising an alkalimetal complexing agent, as described herein, in conjunction with thetreatment of a subterranean formation is that significantly fewerprecautions may need to be taken to exclude alkali metal ions from thesubterranean environment. For example, it may not be necessary toconduct a pre-flush treatment with an NH₄ ⁺—containing treatment fluidprior to acidizing, or fewer pre-flush treatments may be needed. Thiscan reduce the time and expense needed to conduct the acidizingoperation. Likewise, there may be more tolerance for alkali metal ionsin the carrier fluid used to formulate the treatment fluid describedherein, thereby allowing saltier water sources to be used.

Use of a treatment fluid that comprises an alkali metal complexingagent, as described herein, may also significantly expand the breadth ofchelating agents that may be used in conjunction with treating asubterranean formation to sequester metal ions. Specifically, use of analkali metal complexing agent may advantageously allow sodium orpotassium salts of a chelating agent to be used in lieu of the free acidor ammonium salt forms, which may be unknown, not commerciallyavailable, or expensive. In this regard, some of the more commonchelating agents known in the art are available in their ammonium saltforms, but the chelating agents are not biodegradable. In contrast, onlya limited number of biodegradable chelating agents are available intheir free acid or ammonium salt forms. Thus, use of an alkali metalcomplexing agent in the present treatment fluids may allow a widerbreadth of biodegradable chelating agents to be used in conjunction withan acidizing operation, which can improve the environmental profile ofthe acidizing operation and lower the costs associated with thechelating agent. Further discussion of biodegradable chelating agentsfollows hereinbelow.

In some embodiments of the present invention, a crown ether, an azacrownether, and/or a pseudocrown ether may be used as an alkali metalcomplexing agent in conjunction with the treatment of a subterraneanformation. In such embodiments of the present invention, the alkalimetal complexing agent may comprise a cyclic polyether having between 3and 6 ether oxygen atoms present therein. Control of the macrocyclicring size and/or the number of ether oxygen atoms may allow selectivityto be realized in the alkali metal that is complexed. Combinations ofcyclic polyethers having different ring sizes and/or numbers of etheroxygen atoms may be used in the embodiments described herein in order toexpand the breadth of alkali metals complexed. Although any of a crownether, an azacrown ether, a pseudocrown ether, or any combinationthereof may be used in conjunction with treating a subterraneanformation, pseudocrown ethers may be the preferred alkali metalcomplexing agent for some embodiments described herein. Reasons forchoosing a pseudocrown ether and the advantages thereof can includethose noted above.

In some embodiments of the present invention, treatment fluids describedherein may comprise an alkali metal complexing agent comprising a cyclicpolyether having between 3 and 6 ether oxygen atoms present therein. Insome embodiments of the present invention, the treatment fluids mayfurther comprise hydrofluoric acid, a hydrofluoric acid-generatingcompound, or any combination thereof. In some embodiments of the presentinvention, the treatment fluids may further comprise a chelating agent,an alkali metal salt of a chelating agent, a non-alkali metal salt of achelating agent, or any combination thereof.

In some embodiments of the present invention, treatment fluids describedherein may comprise an alkali metal complexing agent comprising a cyclicpolyether having between 3 and 6 ether oxygen atoms present therein; andhydrofluoric acid, a hydrofluoric acid-generating compound, or anycombination thereof. In some embodiments of the present invention, thetreatment fluids may further comprise a chelating agent, an alkali metalsalt of a chelating agent, a non-alkali metal salt of a chelating agent,or any combination thereof.

In some embodiments of the present invention, treatment fluids describedherein may comprise an alkali metal complexing agent comprising apseudocrown ether. In some embodiments of the present invention, thetreatment fluids may have a pH ranging between about 0 and about 8. Insome embodiments of the present invention, the treatment fluids mayfurther comprise hydrofluoric acid, a hydrofluoric acid-generatingcompound, or any combination thereof. In some embodiments of the presentinvention, the treatment fluids may further comprise a chelating agent,an alkali metal salt of a chelating agent, a non-alkali metal salt of achelating agent, or any combination thereof.

In some embodiments of the present invention, treatment fluids describedherein may comprise an alkali metal complexing agent comprising apseudocrown ether; and hydrofluoric acid, a hydrofluoric acid-generatingcompound, or any combination thereof. In some embodiments of the presentinvention, the treatment fluids may have a pH ranging between about 0and about 8. In some embodiments of the present invention, the treatmentfluids may further comprise a chelating agent, an alkali metal salt of achelating agent, a non-alkali metal salt of a chelating agent, or anycombination thereof.

In some embodiments of the present invention, treatment fluids describedherein may comprise an alkali metal complexing agent comprising apseudocrown ether; hydrofluoric acid, a hydrofluoric acid-generatingcompound, or any combination thereof; and, optionally, a chelatingagent, an alkali metal salt of a chelating agent, a non-alkali metalsalt of a chelating agent, or any combination thereof. In someembodiments of the present invention, the pseudocrown ether may becovalently bonded to a polymer.

In some embodiments of the present invention, the treatment fluidsdescribed herein may comprise an aqueous carrier fluid as theircontinuous phase. Suitable aqueous carrier fluids may include, forexample, fresh water, acidified water, salt water, seawater, brine(e.g., a saturated salt solution), or an aqueous salt solution (e.g., anon-saturated salt solution). Aqueous carrier fluids can be obtainedfrom any suitable source. In some embodiments of the present invention,the treatment fluids described herein may comprise an aqueous carrierfluid that is free of alkali metal ions or contains as low aconcentration of alkali metal ions as attainable at a reasonable cost.Choice of a low salt or salt-free aqueous carrier fluid may allow alower concentration of the alkali metal complexing agent to be used inthe treatment fluids, allow saltier subterranean formations to betreated, and/or permit greater quantities of alkali metal salts ofchelating agents to be used. One of ordinary skill in the art will beable to determine an acceptable working level of alkali metal ions thatmay be present in the treatment fluid described herein, given thebenefit of this disclosure. In general, use of an alkali metalcomplexing agent in a treatment fluid may allow greater levity to berealized in choosing an aqueous carrier fluid for an acidizing fluid orother stimulation fluid than would otherwise be possible. In someembodiments of the present invention, the treatment fluids may comprisea carrier fluid that comprises alkali metal ions. In other embodimentsof the present invention, the treatment fluids may comprise a carrierfluid that is substantially free of alkali metal ions.

In some or other embodiments of the present invention, the treatmentfluids may comprise an organic solvent, such as hydrocarbons, as atleast a portion of its continuous phase.

The volume of the carrier fluid to be used in the present treatmentfluids may be dictated by certain characteristics of the subterraneanformation being treated such as, for example, the quantity of siliceousmaterial needing removal, the chemistry of the siliceous material, andthe formation porosity. Determination of an appropriate volume ofcarrier fluid to be used in the treatment fluids may also be influencedby other factors, as will be understood by one having ordinary skill inthe art.

In embodiments of the present invention in which a carrier fluid thatcomprises alkali metal ions is chosen, it is anticipated that at leastan equimolar amount of the alkali metal complexing agent may be includedin the treatment fluids to sequester those alkali metal ions before theyare introduced into a subterranean formation. In some embodiments of thepresent invention, more than an equimolar amount of the alkali metalcomplexing agent may be used in the treatment fluids described herein.More than an equimolar amount of the alkali metal complexing agent maybe used in the treatment fluids, for example, if it is desired tosequester the alkali metals in the treatment fluids and additionalalkali metals in the subterranean formation. In some embodiments, lessthan an equimolar amount of the alkali metal complexing agent may beused in the treatment fluids described herein. Less than an equimolaramount of the alkali metal complexing agent may be used in the treatmentfluids, for example, if it is desired to reduce the level of free alkalimetals in the treatment fluids and/or subterranean formation but notcompletely eliminate them. In some embodiments of the present invention,the treatment fluids may comprise at least about 5% of the alkali metalcomplexing agent by weight. In other embodiments of the presentinvention, the treatment fluids may comprise at least about 10% of thealkali metal complexing agent by weight.

In various embodiments of the present invention, the treatment fluidsdescribed herein may have a pH of about 8 or below. We believe that suchpH values, and especially pH values of about 3 or below, may beeffective for dissolving silicates and/or aluminosilicates in asiliceous formation and/or maintaining dissolved silicon in thetreatment fluids described herein. In addition, in embodiments of thepresent invention in which a chelating agent is present, some chelatingagents may be more effective in forming a metal complex that cansequester a metal ion at certain pH values as opposed to others. In someembodiments of the present invention, the treatment fluids describedherein may have a pH ranging between about 0 and about 8. In otherembodiments of the present invention, the treatment fluids describedherein may have a pH ranging between about 0 and about 6, or betweenabout 0 and about 4, or between about 0 and about 2, or between about 1and about 6, or between about 1 and about 4, or between about 2 andabout 5, or between about 0 and about 3, or between about 3 and about 6.One of ordinary skill in the art will be able to determine an effectiveworking pH for the treatment fluids to satisfactorily maintain siliconin a dissolved state through routine experimentation, given the benefitof this disclosure.

In some embodiments of the present invention, the alkali metalcomplexing agent may comprise a pseudocrown ether. In some embodimentsof the present invention, suitable pseudocrown ethers may have astructure of

wherein, at each occurrence, A independently comprises a carbocyclicring or —CH₂CH₂—; wherein X₁ and X₄ are independently CH₂ or C═O;wherein X₂ and X₃ are independently CH₂, CHR₁, or CR₁R₂; wherein R₁ andR₂ are independently selected from the group consisting of alkyl, aryl,cycloalkyl, or a polymer; and wherein Z is (CH₂)_(n); wherein n is aninteger ranging from 0 to 2; wherein X₂ and X₃ are bonded to one anotherif n is 0. As used herein, the term “carbocyclic ring” refers to anyclosed-chain carbon structure. In some embodiments of the presentinvention, a carbocyclic ring may comprise a cycloalkyl ring. In otherembodiments of the present invention, a carbocyclic ring may comprise aphenyl ring or other type of aromatic ring.

In some embodiments of the present invention, each A may comprise—CH₂CH₂—. That is, in such embodiments of the present invention,suitable pseudocrown ethers may have a structure of

wherein the remainder of the variables are as described hereinabove.

In still other embodiments of the present invention, suitablepseudocrown ethers may have a structure of

wherein B comprises a carbocyclic ring and A and Z are defined as above.In some embodiments of the present invention, B can comprise acycloalkyl ring. In other embodiments of the present invention, B cancomprise a phenyl ring or other type of aromatic ring.

As one of ordinary skill in the art will recognize, crown ethers havingcertain ring sizes are more particularly suited for complexing somealkali metal ions over others. For example, 12-crown-4 maypreferentially complex lithium ions, 15-crown-5 may preferentiallycomplex sodium ions, and 18-crown-6 may preferentially complex potassiumions. One of ordinary skill in the art will recognize that Structures 1,4, and 7 have one less ring oxygen atom than does 12-crown-4. Likewise,Structures 2, 5, and 8 have one less ring oxygen atom than does15-crown-5, and Structures 3, 6, and 9 have one less ring oxygen atomthan does 18-crown-6. Thus, when n is 1, the ring size of Structures 1-9will be analogous to that of the corresponding parent crown ether.Accordingly, it is anticipated that Structures 1, 4, and 7 willpreferentially complex lithium ions when n is 1, Structures 2, 5, and 8will preferentially complex sodium ions when n is 1, and Structures 3,6, and 9 will preferentially complex potassium ions when n is 1.However, it is to be recognized that for n≠1, the selectivity for alkalimetal ion complexation may be different than that of the parent crownether. For example, when n is 2 or 3, Structures 2, 5, and 8 may havesome affinity for potassium rather than sodium due to the larger ringsize.

Various strategies are contemplated for closing the macrocyclic ring inthe foregoing types of pseudocrown ethers. In some embodiments, themacrocyclic ring may be closed by forming the linkage X₂—Z—X₃. In someembodiments, formation of the linkage X₂—Z—X₃ may take place by ahead-to-head or head-to-tail radical coupling of an allyl ether, anacrylate, or a vinyl ether to another allyl ether, acrylate, or vinylether. In some embodiments, ring closing olefin metathesis of an allylether, vinyl ether, or acrylate to another allyl ether, vinyl ether oracrylate may be used to form the linkage X₂—Z—X₃. In some embodiments,an allyl ether, a vinyl ether, or an acrylate may undergo radicalpolymerization, and a radical intermediate may undergo internal radicaltrapping with an allyl ether, a vinyl ether, or an acrylate in order toclose the macrocyclic ring. That is, in such embodiments, thepseudocrown ether may be covalently bonded to a polymer. It is to berecognized that the foregoing ring closure strategies are intended to beillustrative in nature only, and any appropriate synthetic technique maybe used to form the pseudocrown ethers described herein.

In some embodiments of the present invention, the treatment fluidsdescribed herein can comprise hydrofluoric acid, a hydrofluoricacid-generating compound, or any combination thereof. Use ofhydrofluoric acid and/or a hydrofluoric acid-generating compound may beparticularly advantageous when treating a siliceous subterraneanformation or a subterranean formation containing a siliceous material.In some or other embodiments of the present invention, hydrofluoricacid, a hydrofluoric acid-generating compound, or any combinationthereof may be present in a treatment fluid that is separate from atreatment fluid comprising the alkali metal complexing agent. Suitablehydrofluoric acid-generating compounds may include, for example,fluoroboric acid, fluorosulfuric acid, hexafluorophosphoric acid,hexafluoroantimonic acid, difluorophosphoric acid, hexafluorosilicicacid, potassium hydrogen difluoride, sodium hydrogen difluoride, borontrifluoride acetonitrile complex, boron trifluoride acetic acid complex,boron trifluoride dimethyl ether complex, boron trifluoride diethylether complex, boron trifluoride dipropyl ether complex, borontrifluoride dibutyl ether complex, boron trifluoride t-butyl methylether complex, boron trifluoride phosphoric acid complex, borontrifluoride dihydrate, boron trifluoride methanol complex, borontrifluoride ethanol complex, boron trifluoride propanol complex, borontrifluoride isopropanol complex, boron trifluoride phenol complex, borontrifluoride propionic acid complex, boron trifluoride tetrahydrofurancomplex, boron trifluoride piperidine complex, boron trifluorideethylamine complex, boron trifluoride methylamine complex, borontrifluoride triethanolamine complex, polyvinylammonium fluoride,polyvinylpyridinium fluoride, pyridinium fluoride, imidazolium fluoride,ammonium fluoride, ammonium bifluoride, tetrafluoroborate salts,hexafluoroantimonate salts, hexafluorophosphate salts, bifluoride salts,and any combination thereof.

When used, a hydrofluoric acid-generating compound can be present in thetreatment fluids described herein in an amount ranging between about0.1% to about 20% by weight of the treatment fluid. In other embodimentsof the present invention, an amount of the hydrofluoric acid-generatingcompound can range between about 0.5% to about 10% by weight of thetreatment fluid or between about 0.5% to about 8% by weight of thetreatment fluid. Hydrofluoric acid, when present, may be used in similarconcentration ranges.

In some embodiments of the present invention, another acid, anacid-generating compound, or any combination thereof can be present inthe treatment fluids in addition to hydrofluoric acid and/or ahydrofluoric acid-generating compound. In some embodiments of thepresent invention, the additional acid can be a mineral acid such as,for example, hydrochloric acid, or an organic acid such as, for example,acetic acid or formic acid. Other acids that also may be suitable foruse in the treatment fluids include, for example, chloroacetic acid,dichloroacetic acid, trichloroacetic acid, or methanesulfonic acid.Examples of suitable acid-generating compounds can include, for example,esters, aliphatic polyesters, orthoesters, poly(ortho esters),poly(lactides), poly(glycolides), poly(ε-caprolactones),poly(hydroxybutyrates), poly(anhydrides), ethylene glycol monoformate,ethylene glycol diformate, diethylene glycol diformate, glycerylmonoformate, glyceryl diformate, glyceryl triformate, triethylene glycoldiformate, and formate esters of pentaerythritol. Among other things,the additional acid or acid-generating compound can maintain the pH ofthe treatment fluids described herein at a desired low level as thehydrofluoric acid or hydrofluoric acid-generating compound becomesspent. As described below, when a chelating agent is present, theadditional acid or acid-generating compound may also help maintain thepH of the treatment fluids at a level where the chelating agent is moreactive for chelation to take place. In some embodiments of the presentinvention, a mineral acid or an organic acid may be used in treatmentfluids that comprise an alkali metal complexing agent but nothydrofluoric acid and/or a hydrofluoric acid-generating compound.

In some embodiments of the present invention, a chelating agent, analkali metal salt thereof, a non-alkali metal salt thereof, or anycombination thereof may be included in the treatment fluids describedherein. As described above, a chelating agent may be included in thetreatment fluids, for example, when it is desirable to provideadditional sequestration of metal ions (e.g., Group 2 metal ions ortransition metal ions) in a subterranean formation. One of ordinaryskill in the art will be able to choose an appropriate chelating agentand amount thereof to include in a treatment fluid intended for aparticular application, given the benefit of the present disclosure.

In some embodiments of the present invention, the chelating agent may bebiodegradable. Although use of a biodegradable chelating agent may beparticularly advantageous in some embodiments of the present disclosure,there is no requirement to do so, and, in general, any suitablechelating agent may be used. As used herein, the term “biodegradable”refers to a substance that can be broken down by exposure toenvironmental conditions including native or non-native microbes,sunlight, air, heat, and the like. Use of the term “biodegradable” doesnot imply a particular degree of biodegradability, mechanism ofbiodegradability, or a specified biodegradation half-life.

In some embodiments of the present invention, suitable chelating agentsmay include common chelating agent compounds such as, for example,ethylenediaminetetraacetic acid (EDTA), propylenediaminetetraacetic acid(PDTA), nitrilotriacetic acid (NTA),N-(2-hydroxyethyl)ethylenediaminetriacetic acid (HEDTA),diethylenetriaminepentaacetic acid (DTPA), hydroxyethyliminodiaceticacid (HEIDA), cyclohexylenediaminetetraacetic acid (CDTA),diphenylaminesulfonic acid (DPAS),ethylenediaminedi(o-hydroxyphenylacetic) acid (EDDHA), glucoheptonicacid, gluconic acid, citric acid, any salt thereof, any derivativethereof, and the like. It is to be noted that NTA may be considered tobe a biodegradable compound, but it may have undesirable toxicityissues.

In some embodiments of the present invention, suitable chelating agentsmay include biodegradable chelating agents such as, for example,glutamic acid diacetic acid (GLDA), methylglycine diacetic acid (MGDA),β-alanine diacetic acid (β-ADA), ethylenediaminedisuccinic acid,S,S-ethylenediaminedisuccinic acid (EDDS), iminodisuccinic acid (IDS),hydroxyiminodisuccinic acid (HIDS), polyamino disuccinic acids,N-bis[2-(1,2-dicarboxyethoxy)ethyl]glycine (BCA6),N-bis[2-(1,2-dicarboxyethoxy)ethyl]aspartic acid (BCA5),N-bis[2-(1,2-dicarboxyethoxy)ethyl]methylglycine (MCBA5),N-tris[(1,2-dicarboxyethoxy)ethyl]amine (TCA6), N-methyliminodiaceticacid (MIDA), iminodiacetic acid (IDA), N-(2-acetamido)iminodiacetic acid(ADA), hydroxymethyl-iminodiacetic acid, 2-(2-carboxyethylamino)succinic acid (CEAA), 2-(2-carboxymethylamino) succinic acid (CMAA),diethylenetriamine-N,N″-disuccinic acid,triethylenetetramine-N,N′″-disuccinic acid,1,6-hexamethylenediamine-N,N′-disuccinic acid,tetraethylenepentamine-N,N′″-disuccinic acid,2-hydroxypropylene-1,3-diamine-N,N′-disuccinic acid,1,2-propylenediamine-N,N′-disuccinic acid,1,3-propylenediamine-N,N′-disuccinic acid,cis-cyclohexanediamine-N,N′-disuccinic acid,trans-cyclohexanediamine-N,N′-disuccinic acid,ethylenebis(oxyethylenenitrilo)-N,N′-disuccinic acid, glucoheptanoicacid, cysteic acid-N,N-diacetic acid, cysteic acid-N-monoacetic acid,alanine-N-monoacetic acid, N-(3-hydroxysuccinyl) aspartic acid,N-[2-(3-hydroxysuccinyl)]-L-serine, aspartic acid-N,N-diacetic acid,aspartic acid-N-monoacetic acid, any salt thereof, any derivativethereof, or any combination thereof.

When present, the chelating agent or a salt thereof can comprise about1% to about 50% by weight of the treatment fluids described herein. Insome embodiments of the present invention, the chelating agent or a saltthereof can comprise about 3% to about 40% by weight of the treatmentfluid.

When a chelating agent is present in the present treatment fluids, theacid dissociation constants of the chelating agent can dictate the pHrange over which the treatment fluid can be most effectively used. GLDA,for instance, has a pK, value of about 2.6 for its most acidiccarboxylic acid functionality. Below a pH value of about 2.6,dissolution of metal ions will be promoted primarily by the acidity of atreatment fluid containing GLDA, rather than by chelation, since thechelating agent will be in a fully protonated state. MGDA, in contrast,has a pK, value in the range of about 1.5 to 1.6 for its most acidiccarboxylic acid group, and it will not become fully protonated until thepH is lowered to below this level. In this respect, MGDA can beparticularly beneficial for use in acidic treatment fluids, since it canextend the acidity range by nearly a full pH unit over which thechelating agent is an active chelant. The lower pH of the treatmentfluid can beneficially allow for a more vigorous acidizing operation totake place.

In some embodiments of the present invention, an alkali metal complexingagent can be used in combination with other silica scale controladditives in the present treatment fluids. As used herein, the term“silica scale control additive” is any substance capable of suppressingsilica scale build-up by increasing the solubility of dissolved silicon,inhibiting polymer chain propagation of dissolved silicon to produceprecipitates, and/or decreasing the size and/or quantity of precipitatesformed from dissolved silicon. Use of an alkali metal complexing agentin combination with a silica scale control additive may beneficiallyprovide a greater level of dissolved silicon than is possible using aconventional silica scale control additive alone. In addition, use of analkali metal complexing agent may allow a conventional silica scalecontrol additive to be used in treatment fluids that contain at leastsome alkali metal ions and/or in a subterranean formation that containsalkali metal ions. In some embodiments of the present invention,suitable conventional silica scale control additives may include, forexample, phosphonates, aminocarboxylic acids, polyaminocarboxylic acids,polyalkyleneimines (e.g., polyethyleneimine), polyvinylamines,polyallylamines, polyallyldimethylammonium chloride, polyaminoamidedendrimers, any derivative thereof, and any combination thereof.Illustrative commercially available silica scale control additivesinclude, for example, ACUMER 5000 (Rohm and Hass), and CLA-STA® XP andCLA-STA® FS (Halliburton Energy Services).

In some embodiments of the present invention, an alkali metal complexingagent may be used in treatment fluids in combination with a silica scalecontrol additive comprising an ortho-dihydroxybenzene compound (e.g., acatechol). Use of catechols, particularly tannic acid, for silica scalecontrol is described in commonly owned U.S. patent application Ser. No.12/967,868, filed Dec. 14, 2010 and now available as U.S. Pat. No.8,727,002, which is incorporated herein by reference in its entirety.

In some embodiments of the present invention, an alkali metal complexingagent may be used in treatment fluids in combination with a silicatecomplexing agent that comprises a functionalized pyridine compound. Useof functionalized pyridine compounds for suppressing precipitation ofdissolved silicon is described in commonly owned U.S. patent applicationSer. No. 13/444,883 entitled “Treatment Fluids Comprising a SilicateComplexing Agent and Methods for Use Thereof,” filed concurrentlyherewith and now available as U.S. Pat. No. 9,004,168, which isincorporated herein by reference in its entirety.

Use of an alkali metal complexing agent in combination with a silicascale control additive or like agent may be particularly advantageousfor controlling silica scale in a subterranean formation using treatmentfluids, since it is believed that these two materials operate bydifferent mechanisms in inhibiting the production of insoluble siliconmaterials. Without being bound by theory or mechanism, it is believedthat silica scale control additives or like agents may interact directlywith dissolved silicon to increase the solubility of dissolved silicon,inhibit polymer chain propagation of dissolved silicon to produceprecipitates, and/or decrease the size and/or quantity of precipitatesformed from dissolved silicon. One or more different mechanisms may beoperative in a given silica scale control additive, and different silicascale control additives may exhibit different mechanisms. Alkali metalcomplexing agents, in contrast, may complex the alkali metal ions thatcan form particularly damaging silica scale. Thus, by addressing theproblem of silica scale deposition from two different mechanisticdirections, a beneficial reduction thereof may be realized.

In additional embodiments of the present invention, the treatment fluidsdescribed herein may optionally further comprise any number of additivesthat are commonly used in treatment fluids including, for example,surfactants, gel stabilizers, anti-oxidants, polymer degradationprevention additives, relative permeability modifiers, scale inhibitors,corrosion inhibitors, foaming agents, defoaming agents, antifoamingagents, emulsifying agents, de-emulsifying agents, iron control agents,proppants or other particulates, particulate diverters, salts, acids,fluid loss control additives, gas, catalysts, clay control agents,dispersants, flocculants, scavengers (e.g., H₂S scavengers, CO₂scavengers or O₂ scavengers), gelling agents, lubricants, breakers,friction reducers, bridging agents, viscosifiers, weighting agents,solubilizers, pH control agents (e.g., buffers), hydrate inhibitors,consolidating agents, bactericides, catalysts, clay stabilizers, and thelike. Combinations of these additives can be used as well.

In various embodiments of the present invention, treatment fluidscomprising an alkali metal complexing agent may be used in conjunctionwith treating a subterranean formation. More specifically, in someembodiments of the present invention, the treatment fluids describedherein may be used in conjunction with a stimulation operation conductedin a subterranean formation. In some embodiments of the presentinvention, the stimulation operation can comprise a fracturingoperation. In some or other embodiments of the present invention, thestimulation operation can comprise an acidizing operation. In someembodiments of the present invention, such an acidizing operation may beconducted using a treatment fluid that comprises hydrofluoric acid, ahydrofluoric acid-generating compound, or any combination thereof,particularly in a subterranean formation containing silicates and/oraluminosilicates. The silicates and/or aluminosilicates may be naturallyoccurring within the subterranean formation or be introduced during thecourse of treating the subterranean formation.

In some embodiments of the present invention, methods described hereincan comprise: providing a treatment fluid that comprises an alkali metalcomplexing agent comprising a cyclic polyether having between 3 and 6ether oxygen atoms present therein; and hydrofluoric acid, ahydrofluoric acid-generating compound, or any combination thereof; andintroducing the treatment fluid into a subterranean formation.

In some embodiments of the present invention, methods described hereincan comprise: providing a treatment fluid that comprises an alkali metalcomplexing agent comprising a pseudocrown ether; forming a complex ofthe pseudocrown ether with an alkali metal ion; and introducing thetreatment fluid into a subterranean formation. In some embodiments ofthe present invention, the treatment fluid can further comprisehydrofluoric acid, a hydrofluoric acid-generating compound, or anycombination thereof.

In some embodiments of the present invention, the treatment fluid can beintroduced into the subterranean formation before forming the complex.In such embodiments of the present invention, the pseudocrown ether cancomplex alkali metal ions located within the formation. In otherembodiments of the present invention, the treatment fluid can beintroduced in the subterranean formation after forming the complex. Forexample, in such embodiments, the pseudocrown ether may complex alkalimetal ions present within the treatment fluid, possibly arising from achelating agent or other additive, if present. In some embodiments ofthe present invention, formation of a complex between the alkali metalion and the pseudocrown ether may take place both before and after thetreatment fluid is introduced into the subterranean formation.

In some embodiments of the present invention, methods described hereincan comprise: providing a treatment fluid having a pH ranging betweenabout 0 and about 8 that comprises an alkali metal complexing agentcomprising a pseudocrown ether; introducing the treatment fluid into asubterranean formation; and performing an acidizing operation in thesubterranean formation. In some embodiments of the present invention,the treatment fluid can further comprise hydrofluoric acid, ahydrofluoric acid-generating compound, or any combination thereof.

In some embodiments of the present invention, performing an acidizingoperation can comprise at least partially dissolving a portion of thesubterranean formation. In some embodiments of the present invention,the subterranean formation can comprise a siliceous formation, such as,for example, a sandstone formation or a clay-containing formation. Insome embodiments of the present invention, the subterranean formationcan comprise a matrix that is substantially non-siliceous but contains asiliceous material therein (e.g., introduced proppant particulates orsiliceous particulates within a carbonate formation matrix).

In some embodiments of the present invention, the use of an alkali metalcomplexing agent in a subterranean treatment operation may reduce oreliminate the formation of insoluble fluorosilicates or aluminosilicatesduring treatment, relative to a like treatment fluid lacking the alkalimetal complexing agent. As used herein, the term “like treatment fluid”refers to a treatment fluid having a similar composition to anothertreatment fluid but lacking at least one component thereof. That is,treatment fluids described herein may reduce or eliminate the formationof insoluble fluorosilicates or aluminosilicates compared to a treatmentfluid of similar composition that otherwise lacks the alkali metalcomplexing agent.

In some embodiments of the present invention, the treatment fluidsdescribed herein may be used in stimulating a subterranean formation. Insome embodiments of the present invention, such stimulating may comprisean acidizing operation, particularly an acidizing operation conducted ina siliceous formation. In some or other embodiments of the presentinvention, the treatment fluids described herein may be used in othertypes of subterranean treatment operations. For example, in someembodiments of the present invention, the treatment fluids may be usedduring drilling or while remediating a subterranean formation.

When used in conjunction with a stimulation operation, particularly anacidizing operation, an acid (e.g., hydrofluoric acid, a hydrofluoricacid-generating compound, or any combination thereof) may be combinedwith an alkali metal complexing agent in a treatment fluid, in someembodiments of the present invention. That is, the alkali metalcomplexing agent and the hydrofluoric acid and/or hydrofluoricacid-generating compound can be introduced into the subterraneanformation together in such embodiments. In such embodiments of thepresent invention, the treatment fluid may also be used to perform acombined stimulation operation such as, for example, afracture-acidizing treatment, if the introduction pressure issufficiently high. In some embodiments of the present invention, anadditional mineral acid and/or organic acid can be included in additionto the hydrofluoric acid and/or hydrofluoric acid-generating compound,as described hereinabove.

In other embodiments of the present invention, the alkali metalcomplexing agent and the hydrofluoric acid and/or hydrofluoricacid-generating compound may be placed in separate treatment fluids. Insuch embodiments of the present invention, the treatment fluidcomprising the alkali metal complexing agent may be introduced before,concurrently with, or after the treatment fluid comprising hydrofluoricacid and/or a hydrofluoric acid-generating compound. In some embodimentsof the present invention, a treatment fluid comprising an alkali metalcomplexing agent may be introduced into a subterranean formation beforea treatment fluid that comprises hydrofluoric acid, a hydrofluoricacid-generating compound, or any combination thereof. In suchembodiments of the present invention, the subterranean formation can beleft in a condition that disfavors precipitation of alkali metalfluorosilicates once acidizing begins by depleting the formation in freealkali metal ions. For example, a treatment fluid comprising an alkalimetal complexing agent may be used in a hydraulic fracturing operationto create or extend at least one fracture in a subterranean formation.Depending on other operational considerations, other types ofstimulation operations can be conducted prior to acidizing taking place,thereby leaving the formation in a condition that disfavors alkali metalfluorosilicate precipitation once acidizing begins. In some or otherembodiments of the present invention, a treatment fluid comprising analkali metal complexing agent may be introduced into a subterraneanformation after a treatment fluid that comprises hydrofluoric acid, ahydrofluoric acid-generating compound, or any combination thereof. Insome embodiments of the present invention, a treatment fluid comprisingan alkali metal complexing agent and a treatment fluid that compriseshydrofluoric acid, a hydrofluoric acid-generating compound, or anycombination thereof may be introduced concurrently into a subterraneanformation. Optionally, any of these treatment operations can be followedby further treatment operations.

In some embodiments of the present invention, the present treatmentfluids may be used in conjunction with an acidizing operation performedin a subterranean formation, particularly a subterranean formation thatcomprises a siliceous mineral or has had a siliceous material introducedthereto. In some embodiments of the present invention, the subterraneanformation being treated by the acidizing operation can comprise asandstone formation and/or a clay-containing formation. In some or otherembodiments of the present invention, the subterranean formation canhave had a silicate or an aluminosilicate (i.e., a siliceous material)introduced thereto. For example, in a fracturing operation, sandparticulates (a silicate) or a ceramic propping material may beintroduced to the subterranean formation. These introduced siliceousmaterials may be effectively treated according to the methods describedherein as well.

In some embodiments of the present invention, acidizing operations orother stimulation operations conducted using the treatment fluidsdescribed herein may be performed in the absence of an NH₄ ⁺ salt. Asdescribed above, use of an alkali metal complexing agent in treatmentfluids that encounter fluorosilicates or aluminosilicates may allow atleast some alkali metal ions to be present, either in the subterraneanformation or in the treatment fluid. In some embodiments of the presentinvention, the treatment fluids described herein may be substantiallyfree of NH₄ ⁺ ions. In other embodiments of the present invention, thetreatment fluids described herein may comprise an NH₄ ⁺ salt or be usedin conjunction with another treatment fluid that comprises an NH₄ ⁺salt. For example, one might choose to use a treatment fluid comprisingan NH₄ ⁺ salt in conjunction with a treatment fluid comprising an alkalimetal complexing agent if the amount of alkali metal ions in thesubterranean formation is high enough that the alkali metal complexingagent alone cannot effectively reduce or eliminate the formation ofinsoluble fluorosilicates or aluminosilicates when performing anacidizing operation.

In some embodiments of the present invention, the treatment fluidsdescribed herein may be used in treating a particulate pack in asubterranean formation. Particulate packs may include, for example,proppant packs and gravel packs. Treatment of a particulate pack withtreatment fluids comprising an alkali metal complexing agent maybeneficially allow the permeability of the pack to be increased, suchthat it presents a lower impediment to fluid flow.

In some or other embodiments of the present invention, the treatmentfluids described herein may be used in remediation operations within asubterranean formation. Specifically, in some embodiments, treatmentfluids described herein comprising an alkali metal complexing agent maybe used to remove precipitation or accumulation damage within asubterranean formation. As used herein, the term “precipitation oraccumulation damage” refers to a siliceous material that has beendissolved in a subterranean formation and deposited elsewhere within thesubterranean formation.

Therefore, the present invention is well adapted to attain the ends andadvantages mentioned as well as those that are inherent therein. Theparticular embodiments disclosed above are illustrative only, as thepresent invention may be modified and practiced in different butequivalent manners apparent to those skilled in the art having thebenefit of the teachings herein. Furthermore, no limitations areintended to the details of construction or design herein shown, otherthan as described in the claims below. It is therefore evident that theparticular illustrative embodiments disclosed above may be altered,combined, or modified and all such variations are considered within thescope and spirit of the present invention. The invention illustrativelydisclosed herein suitably may be practiced in the absence of any elementthat is not specifically disclosed herein and/or any optional elementdisclosed herein. While compositions and methods are described in termsof “comprising,” “containing,” or “including” various components orsteps, the compositions and methods can also “consist essentially of” or“consist of” the various components and steps. All numbers and rangesdisclosed above may vary by some amount. Whenever a numerical range witha lower limit and an upper limit is disclosed, any number and anyincluded range falling within the range is specifically disclosed. Inparticular, every range of values (of the form, “from about a to aboutb,” or, equivalently, “from approximately a to b,” or, equivalently,“from approximately a-b”) disclosed herein is to be understood to setforth every number and range encompassed within the broader range ofvalues. Also, the terms in the claims have their plain, ordinary meaningunless otherwise explicitly and clearly defined by the patentee.Moreover, the indefinite articles “a” or “an,” as used in the claims,are defined herein to mean one or more than one of the element that itintroduces. If there is any conflict in the usages of a word or term inthis specification and one or more patent or other documents that may beincorporated herein by reference, the definitions that are consistentwith this specification should be adopted.

The invention claimed is:
 1. A treatment fluid comprising: a pseudocrownether; and hydrofluoric acid, a hydrofluoric acid-generating compound,or any combination thereof; wherein the pseudocrown ether has astructure selected from the group consisting of

wherein, at each occurrence, A independently comprises a carbocyclicring or —CH₂CH₂—; wherein X₁ and X₄ are independently CH₂ or C═O;wherein X₂ and X₃ are independently CH₂, CHR₁, or CR₁R₂; wherein R₁ andR₂ are independently selected from the group consisting of alkyl, aryl,cycloalkyl, or a polymer; wherein Z is (CH₂)_(n); wherein n is aninteger ranging from 0 to 2;  wherein X₂ and X₃ are bonded to oneanother if n is 0; and wherein B is a carbocyclic ring.
 2. The treatmentfluid of claim 1, further comprising: a chelating agent, an alkali metalsalt of a chelating agent, a non-alkali metal salt of a chelating agent,or any combination thereof.
 3. The treatment fluid of claim 1, whereineach A is —CH₂CH₂—.
 4. The treatment fluid of claim 1, wherein thepseudocrown ether is covalently bonded to a polymer.
 5. The treatmentfluid of claim 1, wherein the treatment fluid further comprises acarrier fluid comprising alkali metal ions.
 6. The treatment fluid ofclaim 1, wherein the treatment fluid has a pH ranging between about 0and about 8.